A typical automatic transmission for a vehicle includes an oil sump and a variety of rotating components. The oil sump holds hydraulic fluid for use in lubrication, cooling, and hydraulic control of solenoids and valve assemblies within the transmission. The hydraulic fluid typically does not contact the rotating components of the transmission when the vehicle is not experiencing dynamic loading, such as braking, acceleration, or cornering of the vehicle. During dynamic loading, however, the hydraulic fluid within the oil sump may shift so that the rotating components are at least partially submerged in the hydraulic fluid. Submersion of the rotatable components in the hydraulic fluid may drag air into the hydraulic fluid thereby causing fluid aeration and foaming. The air within the transmission case that is dragged into the hydraulic fluid is typically at or near the ambient air pressure of the environment outside of the transmission case due to venting of the transmission case. Fluid aeration and foaming reduce lubrication effectiveness and may cause pressure variations when the hydraulic fluid is later used for transmission lubrication and control.
One method of reducing this aeration and foaming is to use a deeper oil sump so that the hydraulic fluid needs to travel farther to reach the rotating components during dynamic loading. Deeper oil sumps, however, increase the size and weight of the vehicle transmission. Although previous transmissions are functional, new and improved transmissions which exhibit improved performance of hydraulic fluids and controls are desirable. Accordingly, there is a need for an improved transmission that exhibits less fluid aeration and foaming of the hydraulic fluid during dynamic loading of the vehicle.